Created attachment 122868 [details]
Full Dmesg since last reboot

I running Manjaro (Arch based) (4.4.6-1 kernel) on a Dell XPS 13" (9343) with an external displayport (v1.2) 4K@60Hz monitor.

I'm getting several hard lockups per day but this only occurs when I use an external 4K monitor through the display port (i.e. internal laptop display is 100% stable)

I've turned on drm.debug=14 to try to see what is going on, but I do not catch anything on the hard lockups.  

I get quite a bit of display flickering and see these messages in my logs frequently:

Apr 08 12:13:44 station kernel: [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe B FIFO underrun
Apr 09 09:49:56 station kernel: [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe B FIFO underrun
Apr 09 20:55:13 station kernel: [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe B FIFO underrun
Apr 10 16:02:29 station kernel: [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe B FIFO underrun
Apr 11 07:40:40 station kernel: [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe B FIFO underrun
Apr 11 10:12:11 station kernel: [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe B FIFO underrun

Eventually, my machine hard locks right while I'm using it.

I've tried different kernel versions and also set i915.enable_ips=0. I've also tried different 4K monitors and also swapped out my displayport cable.

I'm attaching some files:
* Full dmesg with drm.debug=14 from boot (one lockup occurred at 11:03AM)
* xrandr --verbose
* Xorg.log
* /sys/class/drm/card0/error contains "no error state collected"

Appreciate any ideas.